Plant storage products include starch, lipid and protein. Different plant species differ in the kinds and relative proportions of storage products. Grain seeds, for example, comprise mainly starch, whereas oil seeds comprise mainly oil, and other seeds, such as soybean seeds, comprise mainly protein.
The pathways that produce starch, lipid and protein are connected by key intermediates. For example, hexoses, such as glucose, are precursors of starch synthesis and end products of starch degradation. Hexoses also can be converted to pyruvate, which can lead to (i) the production of acetyl-CoA and malonyl-CoA for fatty acid de novo synthesis, fatty acid elongation, polyketide formation, and isoprenoid synthesis and (ii) the biosynthesis of amino acids.
The ability to alter plant storage products, particularly for crop plants, has been a goal of plant breeders and those employing recombinant DNA techniques. Mike Rankin, a Crops and Soils Agent for the University of Wisconsin (UW), recently reported that Roger Borgers, a soybean specialist with UW has made a good case that low protein soybeans are costing the soybean industry as a whole due to discounted pricing for U.S. soybeans, which are comparatively low-protein, on the world market (World Wide Web at uwex.edu/ces/crops/SoyProtein.htm). According to those at the UW, soybeans from South America are valued more highly, and priced accordingly. Reportedly, one bushel of U.S. soybeans yields 21 pounds of protein and 11.4 pounds of oil, whereas Brazilian soybeans yield 24 pounds of protein and 13 pounds of oil. Rankin opines that more emphasis needs to be put on developing varieties with higher protein content, particularly given that there is a wide variation in soybean protein content within U.S. geographic regions (0.6-2.0%, depending on the year) and among varieties (32.3%-38.1% in Wisconsin). In this regard, the western Corn Belt and Wisconsin do not fare as well as other regions in the U.S., such as the southeast. Significant is that yield is not reduced with higher protein and oil content. In this regard, Baker et al. (Poultry Science 90: 390-395 (2011)) reported that soybean meal produced from high protein or low oligosaccharide varieties of soybeans have a greater nutritional value than soybean meal produced from conventional varieties of soybean and, therefore, could be fed in smaller amounts to broiler chickens.
Recently, the qua-quine starch (QQS) gene (locus ID At3g30720; GenBank Accession Nos. EU805808.1 and NM_113075.4) was found to have an effect on plant biochemical components in Arabidopsis. The QQS gene encodes a protein that contains 59 amino acids, has no known function, has no sequence similarity to other proteins in Arabidopsis or other organisms, has no known catalytic motifs, and no known structural motifs. Analysis of the QQS promoter indicates that it has a CCA1 binding site motif (AAAAATCT) at position −734, a TGA1 binding site motif (TGACGTGG; bZip transcription factor function) at position −504, an UPRMOTIFIAT motif (TGACGTGG; unfold protein response) at position −504, an ABRE-like binding site motif (GACGTGGC; ABA function) at position −503, and an ACGTABREMPTIFA2OSEM motif (ACGTGGC; ABA function) at position −502. QQS RNA transcripts increase during pollen development (from uninucleate microspores to bicellular pollen to tricellular pollen to mature pollen) in WT (WT) Arabidopsis, reaching peak levels in mature pollen. In wild type (WT) Arabidopsis, activity of the QQS promoter as determined using the β-glucuronidase (GUS) gene reporter system is evident at 2 days after imbibition (DAI) in hypocotyls and root tips. As seedlings grow, QQS expression expands to the vasculature, mesophyll cells, hydathodes, and trichomes of leaf blades and petioles. Microscopic dissection indicates no expression is detected in shoot meristem; the dark GUS staining in the shoot tip is associated with the adjacent vasculature. GUS activity is higher in mature leaves compared to young emerging leaves; it consistently appears somewhat unevenly distributed, and is predominantly located in the vasculature; this pattern is maintained throughout development. QQS expression is low in flower buds; however, by flower opening QQS expression is evident in pedicels, sepals, filaments, mature pollen, stigma papillae and styles, but not in petals. During silique development, QQS expression rises in the stigma papillae and style, and becomes apparent throughout the maternal tissues of the silique wall and receptacle. QQS is expressed in roots throughout development. Expression is highest in the root tip, specifically the root cap, columella cells and peripheral cap, and to a lesser extent in the root meristem region, but not in the epidermis. QQS is expressed at the site of lateral root initiation, and in the root tip and vasculature during its emergence; as the lateral root matures, expression remains detectable throughout the root cortex vasculature. GUS activity driven by the QQS promoter was higher in the Atss3 (starch synthase 3) single mutant than in WT under virtually all conditions. Expression was detectable throughout the entire seedling at 2 DAI, as well as later in development, in particular in leaves, flowers and roots. Although the general pattern of expression is similar in the Atss3 mutant and WT, QQS is expressed ectopically in petals in the Atss3 mutant. QQS RNA accumulates neither in the nucleus nor in the plastids. Expression of QQS promoter-GUS in the Atss2/Atss3 double-mutant background was more nuanced, but was in general similar to or somewhat lower than that in WT throughout leaf development. QQS transcripts increased seven-fold during the diurnal cycle in the Atss3 mutant compared to WT Arabidopsis; QQS protein levels also increased in the Atss3 mutant compared to WT Arabidopsis. Analysis of QQS RNAi (interfering RNA) mutants showed that starch content increased 20-30% at the end of the light cycle (about the same increase as observed in Atss3 mutants) due to increased starch biosynthesis and not decreased starch degradation; there was no difference in starch content at the end of the dark cycle. Starch content decreased to WT level within four hours of the dark cycle. All of the above examples are described in Li et al., Plant Journal 58: 485-498 (2009).
In view of the foregoing, it is an object of the present disclosure to provide materials and a method of modifying the amount of at least one biochemical component in a plant. This and other objects and advantages, as well as inventive features, will become apparent from the detailed description provided herein.